Sudden decline of old growth trees this summer

Asked September 26, 2019, 3:31 PM EDT

I have been noticing around town a sudden loss of old growth trees. Several on my block have died suddenly/had their leaves turn brown (within a two months), and I am wondering what can be done to save our remaining old growth trees. I know two culprits that have been named are the ambrosia beetle and inonotus dryadeus (weeping conk). My father has one very old oak that, over the course of the summer, has had all its leaves turn brown. This tree was checked in the spring by an arborist and given a clean bill of health and there are no signs of the weeping conk or ambrosia beetle; the cause of its sudden decline is completely unknown. Are you doing any research on this topic at this time? I am interested in looking for ways to save the great old trees, since they do so much for our neighborhood by means of providing beauty and habitat for local wildlife. Please let me know if you have any resources that could be devoted to investigating and solving this problem/ have ideas on how to proceed. Many Thanks, Julia

Prince George's County Maryland disease issues abiotic issues trees pest insects and mites

1 Response

Hi - Many trees and other plants are showing symptoms of stress now that we are in a period of drought (following a year or extraordinary rain in 2018). We have had many reports of problems with oaks, in particular, this season. Oak trees are in decline all over our region, unfortunately — both red and white oaks. There is no single cause. To occur over many oak species and a wide area points to environmental and cultural causes. Higher summer temperatures are a factor. And yes, a number of people are looking into this issue right now since it is widespread and many trees are affected.

White oaks are intolerant of saturated soil, so last year’s excessive rain is believed to play a role. Red oaks are especially affected by years of drought. Drowning and drought both kill roots. Root stress can lead to early fall coloration, browning, and/or leaf drop and dieback. Trees stressed by unfavorable environmental conditions then become more susceptible to secondary disease issues and pests such as ambrosia beetles and borers. If ambrosia beetles are present, you will see a sawdust-like material (called frass) around the base of the tree or tubes of frass pushed out from the trunk.

Some oaks are dying of bacterial leaf scorch, but this is not common on white oaks. Oak wilt is not active in Maryland generally. Here is more about those diseases: https://extension.umd.edu/hgic/why-oak-trees-are-declining

Take a look at this publication about oak decline. https://extension.tennessee.edu/publications/Documents/SP675.pdf

Most declining oaks are 50-70 years old. Bigger trees need more resources than smaller trees and are less resilient. In addition, many trees are surrounded by turf that intercepts rain and nutrients. Whereas a forest tree’s fallen leaves are entirely recycled into nutrients to feed the tree, homeowners rarely leave those leaves on the ground for trees. Lawn mowing itself can compact soil, so rain and oxygen can’t penetrate well.

There isn’t really much you can do to reverse decline in mature trees. A certified arborist can evaluate the tree for pests and diseases and structural integrity. An arborist can also check to see if there are viable buds on the tree. Find an arborist near you by using the International Society of Arboriculture website: treesaregood.org. Since oaks are premier trees, it’s good to replant oaks (and other types of trees). Be sure to protect saplings from deer.

The other thing that is critical right now is to water the trees that you have access to. Refer to our page about drought conditions, https://extension.umd.edu/hgic/topics/drought-conditions
and watering tips, https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/ornamentals/HG...

Christa